The Twelfth Texas Cavalry served in the Trans-Mississippi as part of Parsons's Brigade throughout the war. The regiment organized for state service on September 11, 1861, at Rockett Springs near Waxahachie. Originally known as the Fourth Texas Dragoons, it became the Twelfth Texas Cavalry Regiment when mustered into the Confederate Army on October 28, 1861. William Henry Parsons, a newspaper editor from Waco, had begun recruiting men shortly after the outbreak of war in April 1861 and was elected colonel. The companies that made up the Twelfth Texas were: Company A, the Hill County Volunteers, recruited in Hill County; Company B, the Freestone Boys, from Freestone County; Company C, the Johnson County Slashers, from Johnson County; Company D, the Bastrop Cavalry Company, from Bastrop County; Company E, the Ellis Grays, from Ellis County; Company F, the Ellis Rangers, made up of the companies of the Texas Mounted Guards from Ellis County and the Texas Mounted Rangers from Parker County; Company G, the Kaufman Guards, from Kaufman County; Company H, the Ellis Blues, from Ellis County; Company I, the Williamson Bowies, from Williamson County; and Company K, the Eutaw Blues, from Limestone County.
Although the men hoped to serve on the east side of the Mississippi River, upon reaching Memphis in May 1862, they were diverted to Little Rock to participate in stopping the Federal advance there. The regiment distinguished itself fighting Federal cavalry during Union Brig. Gen. Samuel R. Curtis's White River Expedition. The Texans' first important skirmish came at the battle of Whitney's Lane on May 19; they also fought in the battle of Cotton Plant on July 7. On August 3, the regiment took part in attacking Curtis's supply line at L'Anguille Ferry and destroyed federal property estimated at half a million dollars. This earned them a reputation for hard fighting. In the autumn of 1862, the Twelfth became the nucleus of a brigade commanded by Colonel Parsons. Early in the war the regiment was led by Lt. Col. John W. Mullen, but after his resignation, Lt. Col. Andrew Bell Burleson generally commanded the men. When the Confederate government dismounted most Texas cavalry near Little Rock, the Twelfth Texas retained its horses because of the distinguished reputation it had garnered fighting Union cavalry. Federal troopers called the Twelfth the "Swamp Fox Regiment," because the men traveled the swamps at night and often attacked Federal positions after dark.
Throughout the war the Twelfth Texas served as scouts and raiders along the west side of the Mississippi River in southeast Arkansas and northeast Louisiana. In mid-1863 the troopers fought in northeast Louisiana with John G. Walker's Texas infantry, raiding Federal depots near Milliken's Bend and Lake Providence in an attempt to help the Confederate defenders at Vicksburg. Their efforts were unsuccessful, and after Vicksburg surrendered in July 1863, the regiment returned to Southeast Arkansas.
The regiment's most significant fighting came during the Red River campaign in Louisiana in the spring of 1864. Although the troopers did not arrive in time to fight at Mansfield and Pleasant Hill, they did attack the Union fleet at Blair's Landing on April 12, 1864. They continued to harass the retreating Federal army under Brig. Gen. Nathaniel Banks and fought in the last battle of the campaign at Yellow Bayou on May 18, 1864.
Following the Red River campaign, the Twelfth Texas returned to southern Arkansas and remained there until ordered to Texas by early 1865. The regiment disbanded on May 23, 1865. Although the troopers fought in few significant battles, their efforts helped prevent a Federal occupation of southern Arkansas and northern Louisiana. As scouts and raiders, they protected East Texas from Federal soldiers and became one of the best known Texas cavalry regiments in the Trans-Mississippi Department.